Vehicle brake



Jan. 15, 1935. A. P. WARNER ET AL VEHICLE BRAKE Original Filed Dec. 22,1926 4 Sheets-Sheet l Jan. 15, 1935. A, p. WARNER :TAL Re. 19,430

VEHICLE BRAKE Original Filed Dec. 22, 1926 4 Sheets-Sheet 2.

VEHICLE BRAKE Jan. 15, 1935. A. P. WARNER ET AL Original Filed Dec.

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A. P. WARNER ET AL Re. 19,430

VEHICLE BRAKE Origixial Filed Dec. 22, 1926 4 Sheets-Sheet 4 3067116725firth/mar P warmer fldcli/ 5 Cadm/ani/ tion or momentum of the vehicle.

Reissued Jan. 15, 1935 Re. 19,430

UNITED STATES PATENT OFFICE VEHICLE BRAKE Arthur P. Warner and AddiBenjamin Cadman, Beloit, Wis., assignors to Warner Electric Brakecliilrporation, South Beloit, 111., a corporation of I 'nois OriginalNo. 1,837,384, dated December 22, 1931, Serial No. 245,714, January 10,1928, which is a continuation of application Serial No. 156,355,December 22, 1926. Application for reissue December 21, 1933, Serial No.703,478

38 Claims. (0]. 188-140) lined and at the same time avoids theoffsetting disadvantages of hydraulic and air brakes.

It is a general object of our invention to provide a vehicle brake whichis superior to any brake now known and which has four outstandingadvantageous characteristics, viz., (a) a brake that requires anegligible amount of physical effort by the driver, (17) one that willproduce an extremely powerful braking force, (c) one that is extremelysensitive, positive and uniform in controllability by the driver, and((1) one which is simple and durable in construction, inexpensive tomanufacture, low in maintenance cost, and is not subject to thenecessity of frequent adjustment to maintain its efficiency.

In carrying out this general object we have devised a vehicle brakewhich includes the braking means proper (herein shown in the form of adrum and a coacting braking device), and a pair of magnetic frictionelements electrically controlled by the driver through suitable meanssuch as a rheostat, said elements deriving power from the motion of thevehicle and being arranged to operate said braking-means throughconnections so constructed as to multiply the force received from saidfriction elements and This invention relates to friction brakes forvehicles and contemplates more particularly an electromagneticallycontrolled brake wherein the braking action is obtained by virtue of themo- The brakes commonly provided on present da automobiles, trucks andthe like have certain well known deficiencies and disadvantages, a briefstatement of which will be conducive to a better understanding of ourinvention.

First, these present brakes are operated by the physical eii'ort of thedriver, which necessitates the use of braking surfaces or linings havingthe highest possible coeflicient of friction in order to obtain sumcientbraking force. The best lining known for this purpose is a fabricmaterial which is relatively soft and therefore wears rapidly,necessitating repeated renewal during the life of the vehicle. Brakesconstructed according to our invention do not depend upon the physicaleffort of the driver but utilize the momentum of the vehicle as a sourceof power which will effect a very powerful braking pressure and for thisreason we are able to use braking surfaces or linings such as metal orhard friction material having a much lower coefficient of friction butgiving vastly greater wear and longer life than the present brakelinings.

Second, brakes now in use are operated from the foot pedal byconnections usually in the form of links, levers, and rock shafts whichadd to the cost of the braking mechanism and which are affected by wear,looseness, springing of the parts, expansion of the brake drums byheating, etc. to such an extent that the braking action variesmaterially and the braking force on the different wheels is unbalanced,thereby requiring frequent adjustment especiallywith four-wheel brakeson automobiles where the front wheels are mounted on pivoted steeringknuckles. Our brake eliminates the necessity for such mechanicalconnections, is unaffected by distortion of the brake drum, andtherefore results in a more perfeet balance of the braking action on thedifferent wheels without the necessity of adjustment.

Some of the difliculties just mentioned are corrected by hydraulicbrakes but the benefits are, to a large extent, offset by disadvantagesincident to the leaking of the liquid, clogging of the ports, etc. Airbrakes also have been used on larger types of vehicles but areobjectionable because of their high cost of installation and maintenanceand the diiliculty of instantaneously and accurately controlling them.Our electric brake corrects the difficulties out- Another object is toprovide a novel vehicle brake wherein the braking force is derivedthrough the frictional gripping engagement of magnetic elements whichare so constructed that they are operable from the usual storage batteryor other source of electrical energy without unduly discharging oroverloading the same under normal conditions of braking.

Still another object is to provide a novel operator in a vehicle brakecapable of deriving variable actuating forcesfrom the momentum of thevehicle, including an electromagnetically controlled friction device thecoacting elements of which are so related that a sensitive operation ofthe device and consequently a graduated braking action is obtainedthroughout the entire range of variation of the energizing current inthe device.

A further object is to provide, in a friction mechanism wherein theaction is governed by the degree of frictional gripping engagementbetween two coacting magnetic elements, means acting to urge saidelements into contact or very close proximity so as to decrease andmaintain substantially constant the reluctance of the magnetic circuitthrough the elements.

Another object is to provide a unitary electrically controlled brakeoperator of the momentum type which is individual to and compactlyassodeliver the increased force to said braking means. Y

ciated with a brake of the usual drum type on a. vehicle wheel, suchassociation being accomplished by so positioning the magnetic frictionelements and force augmenting connections constituting the operatorwithin or in such close proximity to the space normally provided for thebrake structure on said wheel as to avoid interference between the partsof the operator and the wheel, the axle or other parts of the vehicle.

A further object is to provide an electro-magnetically controlled brakeof the momentum type for a dirigible wheel wherein the associated partsof the electromagnetic operator and the braking members are arranged ina compact unit which is operatively disposed about a free open axialspace of sufficient dimensions to accommodate the usual yoke typesteering knuckle construction without disturbing the normal relationbetween the plane of rotation of the wheel and the pivotal axis of theknuckle, and without material increase in the dimensions of the brakestructure relative to the diameter of the wheel.

Another object is to provide an electricallycontrolled momentum brakefor vehicles which will respond instantly and uniformly to theapplication of current thereto and produce a braking action determinedsolely by the strength of said current, and which has means foreffectually restoring its operating parts to normal position after thecurrent flow has been cut off so as to quickly and reliably release thebrake.

It is also an object of this invention to provide of one revolution ofthe wheel following the energization of the electric control means.

Other objects and advantages of the invention will become apparent fromthe following description taken in connection with the accompanyingdrawings, in which:

Figure l is a fragmentary view in vertical section of a vehicle wheelequipped with an electric brake embodying the features of the presentinvention.-

Figs. 2 and 3 are sectional views taken respectively along the lines 22and 3-3 of Fig. 1.

Fig. 4 is an enlarged sectional view on the line 44 of Fig. 2. v

Fig. 5 is a diagrammatic view of the electrical control circuit for thebrake.

Fig. 6 is a view in vertical section of a dirigible vehicle wheelsupporting a pivoted axle and equipped with an electric brake embodyingthe present invention, as seen on the plane of the line 6-6 in Fig. '7.

Fig. '7 is a side elevation of the brake structure shown in Fig. 6 witha portion of'the struc it the invention to the specific form disclosedbut intend to cover all modifications and alternative.

constructions falling within the spirit and scope of the invention asexpressed in the appended claims. I

Generally stated, the present invention includes friction braking means,preferably of the shoe or band type, and a magnetic friction operatortherefor controllable by the vehicle driver by regulating the flow ofcurrent thereto from a storage battery or other source of electricenergy on the vehicle to be braked, the operator being adapted whenenergized to derive energy from the motion or momentum of the vehicleand to apply this energy to said braking means with increased mechanicaladvantage. The operator, in the embodiments selected for the purpose ofillustration, is individual to the brake on one vehicle wheel andincludes a friction device composed of two magnetic friction elements,one rotatable with the vehicle wheel, the other being operativelyconnected to the braking means through a force-augmenting mechanism forsetting the brake upon limited oscillation of the driven element ineither direction from its brakereleased position in which it is normallymaintained. An electromagnetic winding forms, with one of said elements,an efiicient electromagnet which, when energized, causes frictionalgripping engagement of the elements, with a force proportional to thestrength of the energizing current. The driven element being thusmagnetically attracted to the rotating element, is carried alongtherewith for a short angular distance, thereby actuating theforce-multiplying mechanism to operate the braking means. When the brakebecomes set, the unity of motion of the elements is broken and theresulting frictional slippage between the elements allows for furtherrotation of the driving element which holds the driven element inbrake-setting position so long as the elements remain magnetized, butupon the interruption of the energizing current the parts of theoperator are quickly restored to brake-released position. This may takeplace after the vehicle has come to rest or its speed reduced to theextent desired by the driver.

To describe the exemplary form of the invention more particularly,reference will first be made to Figs. 1 to 5 of the drawings wherein adrum brake of the internally expansible type is illustrated inconjunction with a standard vehicle wheel mounted on the end of a deador stationary axle 6, the size and shape of which is determined by theweight and type of the vehicle on which the axle is employed. Herein thewheel is shown as comprising spokes 7 secured between flanges 8 of a hub9 which is rotatably mounted in the conventional way through hearings ontheend or spindle 10 of the axle. A nut 11 threaded onto the spindleserves to hold the wheel in position on the axle. This type of wheel andthe bearing therefor, thus selected to illustrate the present brake, arecommonly employed on heavy duty vehicles such as trucks having dead rearaxles and trailers, but the brake may be equally well adapted for use onwheels mounted on driving axles, or on pivoted steering knuckles such asare more commonly employed on passenger vehicles. Such adaptation topassenger vehicle wheels is. shown in Figs. 6 to 8, fully describedhereinafter, wherein the exemplary form of the invention is associatedwith a wheel mounted on a pivoted steering knuckle of a type commonlyused on the dirigible front wheels of automobiles.

Mounted on the inner side of the wheel so as to rotate therewith is arevoluble member in the form of a drum 12 disposed concentrically withrespect to the axis of the wheel and having a diameter substantiallyless than that of the wheel. Herein the drum has an inturned flange 13at its outer end which is bolted or otherwise secured to the inner hubflange 8. If desired, the drum may be lined with a strip 14 preferablyof metallic material providing an internal peripheral braking surface.

In the present instance, the inner or open end of the drum is closed bya substantially flat disk member or casing 15 received on the axle 10adjacent the inner end of the hub 9 and firmly held against rotation asby keying anintegral hub portion 16 thereof to the axle. The casing maybe reinforced by radially extending internal ribs 17 joined at theirouter ends by a peripheral flange 18.

The gripping devices or shoes which constitute the non-rotatable part ofthe brake and which are adapted to engage frictionally with the internalsurface of the lining 14 to eifect the braking action, may be of anypreferred construction. the ones illustrated in Fig. 3 being segmentalin form, each comprising an arcuate backing portion 19 reinforced by aninternal rib 20. Preferably, a covering 21 of suitable material issecured to each shoe as by means of bolts. Because of the enormousbraking force available with the present power brake, the coverings maybe made of metal or other material having a lower friction coefficientbut greater resistance to wear and deterioration by heat than ordinaryfabric brake linings. A covering material known to the trade as brakeblock and having substantially thesame friction properties as steel butmore resistant to wear has been found to give the desired brakingaction. The use of such frictional material positively eliminates thewell known annoyance called squeaking which is prevalent in brakeshaving fabric linings.

The brake shoes are arranged in end to end relation within the drum andfirmly held against rotation, at the same time being freely expansible.To this end, the rib 20 of each shoe is formed intermediate its endswith a radially extending flanged recess 22 which flts over a squaredbushing 23 extending parallel to the drum axis and secured by bolts 24passing through apertured bosses formed on the vertical ribs of thecasing 15.

Associated with the adjacent end portions of the brake shoes in Fig. 3are suitable expanding devices which, when actuated, are adapted tospread the shoes apart and thus press the coverings -,21 into brakingengagement with the lining 14. In

the present instance, these devices comprise cam blocks 26 mountedbetween the ends of the shoes to oscillate on fixed axes which extendparallel to and are spaced a substantial distance from the axle 10. Tothis end, the blocks are formed integral with or otherwise rigidlysecured to rock-. shafts 27 and 28 which'are journaled intermediatetheir ends in bosses formed at opposite ends of the horizontal casingrib 17. Each block 26 is composed of hardened steel and is ofsubstantially rectangular shape so that upon oscillation in eitherdirection from the normal brake-released position shown in Fig. 3, theremote corners will bear against and spread the opposed webbed ends 25of the shoes. Contractile springs 2'7 anchored to the shoes serve tocontract the shoes within the drum as permitted by the angular positionsof the cam blocks. Since the expanding devices thus provided are offsetor located eccentrically with respect to the axle 10 and near theperiphery of the drum, they are not limited in size, shape or degree ofmotion by the axle and wheel hub or by the usual steering knuckle whenthe brake is applied to a dirigible wheel as in Figs. 6 to 8.

be made simpler and more reliable.

Thus, the blocks may be constructed short enough to give the desiredexpansive force on the brake shoes for a small oscillation of the rockshafts and yet long enough to prevent wearing or rounding off at theirends under the operating conditions normally encountered in service.

That part of the operator which is adapted to convert a portion of theenergy available by virtue of the momentum of the vehicle when in motioninto a form which may be utilized for actuation of the brake expandingdevices comprises two friction elements which may be drawn into firmgripping engagement by the energization of an efficient electromagnet.One of these elements is arranged to rotate in unison with the wheel towhich the brake is applied and in the form herein illustrated comprisesan external peripheral flange 29 formed integral with or otherwisesupported by the drum so as to present a plane annular surface ,whichfaces inwardly from the wheel and is substantially flush with the openend of the drum., Thus, in the present instance, the radial width ofthis surface is relatively small and its diameter is slightly largerthan that of the drum.

The friction surface of the other element is of the same diameter as theflange 29 and preferably is on a substantially rigid ring 30 receivedloosely upon an external bearing surface provided by the flange 18 ofthe casing 15. A floating mounting is thus provided for the ring whichholds the ring firmly in coaxial" relation with respect to the brakedrum at the same time allowing for oscillation of the ring about thedrum axis. Such mounting also allows for, approaching movement of thering in an axial direction toward the flange 29 to permit of frictionalengagement between its flat surface and the friction surface of theflange 29. The ring is of such narrow radial width and spaced soremotely from the axle 6 that it is relatively light in construction anddoes not preclude the expanding devicesor other parts of the brakingmeans proper from being simply constructed and mounted in the usual way.

To exclude dust. and dirt from the friction surfaces between theelements and the bearing surfaces between the ring 30 and the casing15,an annular member 31 constituting an extension of the casing 15 andcarried thereby is formed with a peripheral flange 32 enclosing the ringand overlying the flange 29. Means such as adjusting screws 33 may beprovided to hold the ring 30 adjacent the flange 29 but preferably notso close as to allow any portion of the ring to become wedged betweenthe ends of the screws and the rotatable flange 29 due to the slightlateral wobbling of the flange during rotation.

In the-preferred form of the invention, the two friction elements areformed of magnetic material and constitute the core and armature of apowerful electromagnet which is capable of producing the necessarygripping action when energized with a comparatively small current suchas can be safely drawn from the ordinary storage battery on a vehiclewithout unduly discharging the'same. While either of the elements may beconstructed to constitute the magnetic core, it is preferable that thering 30 serve this purpose because the electrical connections theretomay Herein the ring 30 carries a winding or coil 34 comprising aninsulated conducting wire wound continuously in a series of annularturns to form a single annulus which is snugly mounted in an annulargroove formed in the ring 30 centrally of its friction surface. Thegroove may be closed by a 1 on modern self-propelled'vehicles and evenif.

ring 35 of non-magnetic material thereby tightly sealing the coil 34withinsthe ring 30. With the magnet thus constructed, the twoconcentrically arranged portions of the flat friction surface on thering constitute pole faces of oppositely polarity between which amagnetic flux flows whenever the winding is energized. The area of thefriction face of the magnet and the ring 35 which also presents afriction surface is such as to properly distribute frictional wear andto provide for the rigidity of the magnet structure when gripping therotating flange or armature. To lighten the magnet and still leave anample path for the flow of fiux through the magnetic circuit, the backportion of the ring 30, in the form illustrated, is cut away at itsinner and outer peripheral edges.

In operation, the initial flow of current in the magnet winding producesa flux which flows in a mean path indicated approximately by the dottedline 36 in Fig. 4, thereby causing magnetic attraction to the rotatableflange armature. The force thus produced acts in an axial direction todraw each elemental portion of the magnet ring firmly against the flange29. Such intimate gripping engagement may involve slight yielding ofportions of the flange 29 or the ring 30. The frictional force resultingfrom the gripping engagement of the magnetic elements tends to producecontinued movement of the driven element or ring along with the rotatingflange and the magnitude of this force is equal to the product of thenormal pressure or magnetic attraction and the friction coefllcientbetween the coacting surfaces.

The present magnet is extremely efiicient in its operation, that is tosay, a maximum attractive force is obtained with a minimum number ofampere turns effecting economy in manufacture and with a minimum currentconsumption. For example, with a magnetconstructed for use in a brakefor a ten-ton freight-hauling vehicle and having a coil of sixty-threeturns, an attractive force of four thousand pounds is exerted when thecoil is energized with a current of 4.75 amperes to give a maximumapplication of the brake. This current consumption may be compared tothe rate of consumption of from 7 to 10 amperes in the averageautomobile lighting system and the rate of consumption in a vehiclestarting motor while running of approximately 100 amperes. For use inthe brakes of lighter passenger cars, each brake magnet can be designedto draw a current of less than one ampere for maximum brake applicationand less than one-half ampere for ordinary braking. Thus, the flow ofcurrent vto ,give maximum braking at all four wheels of drawn frequentlyfrom the battery, would not unduly discharge the same.

Among the factors to which the high efficiency of the present magneticfriction device may be at- 1 tributed are the substantial elimination ofan air gap between the magnetic poles and the armature by means to belater described, the short length of the flux circuit, and theutilization of all availvable flux lines produced by the magneticwinding. The two features last named result from the use An importantadvantage accruing from the use of friction elements which are broughtinto gripping engagement by a force acting in an axial direction is thatthe operation of the elements and therefore the control of the brakingaction is not materially affected by expansion of the drum by the heatdeveloped in braking the vehicle. In other words, since the coactingfriction surfaces are disposed radially or perpendicular to the drumaxis, variation in diameter of the rotating or driving element byheating does not change the operative relation of the elements.Moreover, such axial engagement does not produce an end thrust on thevehicle wheel, because the gripping force originates within instead ofexternally of the coacting elements.

The winding 34 for controlling the operation of the friction operator isintended to be energized from the usual storage battery 37 (Fig. orother source of current at substantially constant potential and the flowof current through the windings of the brake magnets .of the severalvehicle wheels may be accurately varied in successive increments by ahand or foot operated control device such for example as a pedal 38, themovements of which operate a suitable rheostat 39. The energizingcircuit for the magnet winding is indicated diagrammatically in Fig. 5and preferably extends from the grounded battery terminal through aconductor 40 comprising, the vehicle frame, the axle 10, the casing 15and the ring 30 which is electrically connected to one terminal end ofthe winding 34. The other battery terminal is connected to the rheostat39 which in turn is connected to the other winding terminal through aninsulated conductor including a wire 41 and. suitable means to allow foroscillation of the magnetic ring 30, this being accomplished in thepresent instance through the medium of the wiping contact constructionshownin Fig. 4. For this purpose, an arcuate strip 42 of insulatingmaterial is mounted on the back of the ring 30 and carries a metalliccontact strip 43 connected to the insulated terminal of the winding 34.Mounted on the closure member 31 is a junction'box 44 of insulatingmaterial providing a recess in which a reciprocable brush 45 is mountedin position to contact the strip 43 substantially centrally thereof whenthe ring 30 is in normal or brake-released position. A compressionspring 46 encircling a shank 47 on the brush and acting between thebrush and the end of the brush recess constantly urges the brush intocontact with the strip 43. Thus, the brush is adapted to contact thestrip continuously throughout the range of oscillation of the magnetring 30 in either direction despite any lateral wobbling of the flangearmature 29 in its rotation. The conductor 41 leading from the rheostat.may be secured to the vehicle chassis with its remote end extending intoand stationarily supported by the junction box 44 for connection withthe brush 45. Thus a simple and flexible connection is provided betweenthe brake control means and the actuating mechanism on the vehicle wheelwhich connection replaces the heavy and usually complicated mechanicalor hydraulic operating connections now in common use on automotivevehicles for transmitting the braking force to the several brakes fromthe common source of braking power.

It should be observed in passing that with the means herein contemplatedfor controlling the present friction operator, very little physicaleffort on the part of the vehicle driver is necesany in order to set thebrakes. Furthermore, since only a slight movement of the driver's footis required to close the circuit through the magnetic winding ascompared to that required to operate a standard brake foot pedal, thepresent control device can be so closely associated withthe acceleratorof the vehicle as to materially reduce the time required for thedriver'to withdraw his foot from the accelerator pedal and place it onthe brake control pedal, thereby materially reducing the time requiredto initiate the application of the brakes.

The force made available by energizing the magnet of the frictionoperator when the vehicle is in motion may be applied with increasedmechanical advantage to either or both of the expanding devices forsetting the brake. The mechanism herein employed for thus augmenting thefrictional force is adapted to actuate the rock shaft 2'7 in eitherdirection and includes a substantially straight crank arm 48 rigidlyfixed as by keying to the end of the rock shaft which is located outsideof the casing 15. The crank thus being free to oscillate in a verticalplane disposed outside of the drum and adjacent the ring 30 may be madeof a length substantially equal to the radius of the ring 30 and thusadapted to provide a moment arm of maximum length for the forceavailable at the driven friction element. As a means for operativelyconnecting the driven element to the crank, a link 49 may be employed,said link being pivotally connected at one end to the outer or free endof the crank and at its other end to a stud 50 outside of the casingmember 31. The stud may be anchored in the ring 30 as by threading intoa boss 51 so as to project through an arcuate slot 52 in the member 31,allowance being thereby made for the necessary oscillation of the magnetin either direction.

Preferably the length of the link 49 is such as to hold the crank 48 inperpendicular relation with respect to a diameter including the axes ofthe drum and the rock shaft 27 when the ring 30 is in normal or brakereleased position as shown in Fig. 2. Thus the actuating force appliedto the crank by the driven friction element acts tangentially of thering 30 and in a direction perpendicular to the crank so that its momentarm is substantially equal to the radius of the ring regardless of thedirection in which the crank arm is oscillated. The crank arm 48 and thecam block on the rock shaft 27 constitute in effect a bell crank leverwhich is capable of transmitting the actuating force to the brake shoeswith a mechanical advantage which is equal approximately to the lengthof the crank arm 48 divided by the radial distance between the axis ofthe rock shaft 27 and the remotest point of contact between the ends ofthe shoes and the expanding cam block. In the brake shown in Figs. 1 to3, as designed for a ten-ton road vehicle, this ratio is approximately17 to 1 so that with a frictional force of 1000 pounds (which isproduced by an attractive force of 4000 pounds between the frictionelements when a current of 4.75 amperes is passed through a coil of 63turns, as heretofore explained) the brake shoes will be expanded with aforce of approximately 17,000 pounds.

It will be observed that the operating parts of the force-multiplyingconnection between the driven friction element and the brake shoes areso constructed and arranged that the proper degree of mechanicaladvantage is obtained in.

spite of the fixed structural relation which exists in theconventionaldrum type of brake between the axle, the brake drum, and the enclosingcasing therefor. Thus by arranging the crank arm 49 so that it extendsin a non-radial direction, that is, at an angle to a diameter passingthrough the axes of the drum and the rock shaft 27, the length of thearm may be substantially greater than the distance between the axle andthe rock shaft 27 and therefore such as to actuate the expanding devicewith the desired leverage. By directly associating the movable parts ofthe expanding device with the end portions of the brake shoes, they maybe so coordinated structurally with the crank arm that suflicientmultiplication of the actuating force is obtained through the combinedaction of the crank and the expanding device. Furthermore, all of theparts of the force multiplying connections are located so remotely fromthe axle, and their ranges of movements in either direction to apply thebrake are such that their operation is not interfered with by the usualsteering knuckle when the present brake is adapted to a dirigible wheel,as shown in Figs. 6 and 7. a

An inherent characteristic of brakes wherein the actuating force isderived from the momentum of the vehicle is that further movement of thevehicle is required to set the brake following the operation of thedrivers control device. Therefore, in adapting the momentum principle ofoperation to a brake for a modern automotive vehicle which must respondinstantaneously to the drivers control, a movement of the vehiclecorresponding to only a small fraction of a revolution of the vehiclewheels is allowable for operating the brakes. This result isaccomplished in the present instance by employing a magnet capable ofexerting an attractive force of large magnitude; by magnifying thefrictional force without unnecessary loss of motion; and by operatingthe augmenting mechanism at a point as remote as practicable from thedrum axis. With such a large attractive force as may be obtained by thepresent magnet, only a moderate multiplication of the frictional forceproduced is necessary in order to give the required expansive force atthe brake shoes. The angle through which the magnet ring must move totake up the normal clearance between the shoe coverings and the drumlining is accordingly lessened since the reduction in motion through thecrank and the expanding device is proportional to the magnification ofthe force. The lineal movement of a point on the magnet ring beingproportional to the distance from the drum axis, the movement of thevehicle required to take up the shoe clearance is further reduced in thepresent instance by providing a driving friction surface ofcomparatively large diameter, in the present instance slightly greaterthan that of the drum.

By combining these various factors, the angular movement of the wheelwhich is required to set the brake following the energization of themagnet is practically negligible, corresponding in the present instanceto a motion of the vehicle of approximately two inches.

Another advantage of the present force-multiplying mechanism is that itsoperating parts have a wide allowable range of movement so that wear onthe shoe coverings is automatically taken up on each brake application,thereby making the brakes practically self-adjusting, and eliminatingthe annoyance and expenses incident to the mainring 30 toward the flange29.

tenance of proper adjustment in ordinary manually operable brakes.

. In the present arrangement, the outer end of the crank 48 projectsslightly beyond the circumference of the drum flange 29 and preferablyis protected by a casing having a flat enclosing wall 52 and aperipheral flange 53 secured as by bolts against the closure member 31and an extended portion thereof. This casing completely encloses thatportion of the force-multiplying mechanism which is located outside ofthe drum closure and is of such size and shape as to allow for propermovement of the operating parts and for clearance.

The attractive force which may be produced with a ring magnet of theabove character, especially when it isto be energized from a storagebattery or other source of relatively small capacity, isgreatly-impaired by the presence of a substantial air gap between themagnetic core and armature and varies to a marked degree with slightchanges in the width of the gap. Such a condition, were it to exist in afriction operator of the present character, would be particularlydisadvantageous in that it would preventsensitive control of the brakingaction which is a desirable feature of brake control in automotivebraking systems. For example, with an air gap of a given width betweenthe magnetic elements, a current of such magnitude might be required todraw the elements into contact that excessive braking action wouldresult by the greater attractive force and therefore the greaterfrictional force produced after closure of the magnetic circuit by suchcontact. Thus, the reluctance of the magnetic circuit would be avariable quantity, and the driver of the vehicle, not being able to gagethe reluctance at any given time, would be unable to so regulate thecurrent flow as to produce the intended deceleration of the vehicle.Various factors would tend to aggravate this difficulty in an operatorof the present character, because of the normal relative rotationbetween the magnetic elements. Among these factors is the fact that thebrake is subject to the severe strains and constant jarring incident tothe use of the brake on an automotive vehicle. Other factors are theinherent lateral wobbling of the drum flange 29 due to inaccuracies inconstruction and mounting of the vehicle wheel and drum and to loosenessand wear of the parts, and the fact that it is practically impossible toform the friction surfaces on the magnetic elements in true geometricplanes.

All of these difiiculties haveibeen effectively overcome in the presentbrake by establishing such close association and constant relationshipbetween the magnetic friction elementsthat the magnetic circuit throughthe elements is substantially closed at the time when the magnet becomesenergized to set the brake. This is accomplished in the present instanceby maintaining intimate mechanical contact between said frictionelements at all times, and the means employed for this purpose comprisesthe coiled spring 46 (Fig. 4) which acts through the brush 45 toresiliently urge one side of the magnetic Thus the spring acts tomaintain the coacting surfaces of the elements in mechanical contact,thereby substantially closing the magnetic flux circuit at one or morepoints in spite of the inherent wobbling of the drum flange duringrotation. With an initial metallic path of such low reluctance, a largemagnetic flux and therefore a strong 'hicle driver.

magnetic force will be developed upon the energization of the windingeven with the minimum current which may be supplied by the rheostatcontrol, and any portions of the magnet ring not then in contact withthe flange will be drawn i.n stantaneously against the flange, therebycompletely closing the flux circuits around the entire periphery of themagnet. Thus, gripping engagement of the magnetic elements will beeffected by such a small current in the magnetic winding that the samecurrent will not produce excessive braking after complete closure of themagnetic circuit by the engagement. In this way the uncertainty orvariation in the action which would result from a substantial air gapbetween the elements is eliminated, and the braking action is governedsolely by the strength of the energizing current, so that the driver hascomplete control of and can accurately and uniformly regulate thedeceleration of the vehicle over the entire range of current variationby the" control means.

Means supplemental to the springs 2'7 is pro- .vided for normallyholding the parts of the friction operator against movement in eitherdirection by reason of any frictional engagement between the magneticelements, and for quickly and reliably restoring the parts tobrake-released position upon de-energization of the magnetic winding. Inthe present instance, this means comprises a spring 54 of the hairpintype mounted within the auxiliary casing on a stud 55 which projectsoutwardly from the member 31. The spring has an end 56 which is heldfixed between a stationary pin 57 and the flange 53 and another end 58which is movable and positioned between opposed lugs on a lateralextension 59 integrally formed on the crank arm 48. Normally, that iswhen the crank arm is in brake-released position, the spring is notunder stress, but it is tensioned by flexure' of the end 58 duringoscillation of the crank in either direction. Then, when the winding isde-energized to release the brake, the spring operates to restore thecrank and the parts operatively connected thereto to the normal positionshown in Fig. 2. Since the force thus exerted is applied to the crankarm at a substantial distance from its axis, the force will be ample toovercome the normal frictional engagement between the magnetic elementsand any adherence of the elements such as that due to residualmagnetism.

To provide an auxiliary brake for use as an emergency or parking brake,the rock shaft 28 and the expanding cam thereof may be arranged formanual operation. For this purpose a crank arm 60 is fixed to the shaft28 outside of the casing 15 and connected through mechanism including arod 61 to a hand lever or other operating means located within the reachof the ve- Thus, the same shoes are adapted to be actuated either by theelectrically controlled momentum actuating mechanism or by manualoperation. When the electrically controlled brake is applied to thedirigible wheels of a vehicle, the manual operating means wouldpreferably be omitted.

Referring now to Figs. 6 and 8 which show the brake applied to the frontor dirigible wheel of an automobile, the general arrangement of theparts and their functional relationship are substructure withoutinterfering with the normal operation thereof or necessitating anychange in its structure or its conventional relationship to the wheel.

As illustrated in Fig. 6 the vehicle wheel comprises a disk '7 securedupon a flange 8 of the hub 9 mounted on a spindle 10, the hub beingprovided with conventional antifriction bearings. The spindle 10 isintegral with a yoke or steering knuckle 62 .of conventionalconstruction and pivotally supported upon the adjacent end of thestationary axle 63 by means of the pivot pin 64. A conventional steeringarm 65 is provided, preferably integral with the spindle yoke orsteering knuckle 62, and controlled by a. drag link 66 pivoted thereonfor manual operation in a well known manner, not shown herein. The disk'7 supports upon its outer periphery a conventional rim 67 which carriesa pneumatic tire 68.

The brake drum 12 has a mounting flange 13 secured to the hub flange 8for rotation with the wheel, the open inner end of the drum beingsubstantially closed by an annular disk member 15 rigidly mounted on asuitable flange 16 provided on the spindle portion of the steeringknuckle.

The braking members comprise shoes 19* similar to those previouslydescribed and similarly arranged within the drum except that the shoesare held against rotation and at the same time mounted for expansiblemovement by being pivotally secured at one adjacent pair of the ends ofthe respective shoes upon pivot studs 69 rigidly mounted on the casing15 and extending through suitable bearings in the adjacent ends of thebrake shoes.

A single cam block 26 is positioned between the opposite adjacent endsof the pivoted brake shoes, the cam block being fixed in relation to arock shaft 28 having a suitable bearing support in the stationary casingmember 15 Oscillation of the cam block in either direction efiects thespreading of the shoes into frictional braking contact with the drum 12in similar manner to that previously described, the shoes beingresiliently retained in contact with the cam block by a spring 27oppositely attached to the respective shoes.

It will be here noted that the arrangement of the shoes, together withtheir pivotal supports and expanding cam, is substantially confinedwithin a narrow annular space immediately adjacent to the periphery ofthe drum and affording a large clear space about the axis of the wheelwherein there is ample room for the location and normal operation of thesteering knuckle and the steering arm extending therefrom.

In the present arrangement the armature element 29 of theelectromagnetic brake actuating members is spaced from the inner edge ofthe drum 12 and positioned substantially nearer the edge of the drumnext to the wheel, preferably.

being integral with the drum structure. The magnet core element 30,carrying a conductor winding 34 and constructed as previously described,is positioned about the inner portion of the drum. Immediately outwardof the peripheral edge of the flange 29 is provided an annular flange 31integral with or rigidly secured tothe casing 15, and providing an outerhousing for the magnet ring 30 the flange 31 and inner end of the drum12 forming an annular chamber for floating retention of the core member30 wherein the latter may move axially to and from its complementaryarmature member 29*".

The magnetizing winding is energized through a conductor 41 associatedwith a brush structure such as is illustrated in Fig. 4, and whichfunctions also to maintain mechanical contact at at least one pointbetween the ring 30 and flange 29*, as previously described herein.

The operating connections between the oscillatory magnet ring 30 and thecam block 26 are similar to that hereinbefore described and comprise astud 50 mounted on the ring 30 and extending through a suitable slot inthe casing 15, the stud 50 being pivotally connected by the link 49 withthe free end of a crank arm 4:8 rigidly secured upon the rock shaft 28*.By this means the oscillatory movement of the magnet ring 30 effects theoperative movement of the cam block 26 and the application of the brakesin similar manner and with similar effect to that previously described.The elements of the operator and the brake shoes are maintained in brakereleased position, when the magnet is deenergized, by means of thespring54 positioned and connected as previously described.

It will be noted that the construction disclosed in Figs. 6 to 8provides a very compact unitary arrangement of the brake members andparts of the operator which is readily adaptable to mounting upon adirigible wheel wherein ample space must be provided for the locationand operative movement of the steering knuckle construction common tosuch wheels and wherein the pivotal axis of the steering knuckle may bemaintained in the close proximity to the plane of rotation of the wheelnecessary to the ease in steering with safe support which has beendetermined by previous practice.

It will be seen that the adaptability of the elements comprising thepresent invention to arrangement in compact unitary relation in asubstantially annular space about a clear central space defined by thedimensions of the usual steering knuckle structure, is important insecuring the advantages residing in the present invention to four wheelinstallations of vehicle brakes. It will also be seen that the actualpower for setting the brake is created within the brake unit itself bythe action of the electromagnetic friction device 29, 30, which derivesforce from the rotating wheel and transmits the force to the brakingmeans, the conductor 41 constituting the sole connection between theunitary brake structure and the driver's control pedal or lever, thuseliminating all mechanical levers and linkage for this purpose.

Summarizing the characteristics of our invention, as they will now beunderstood from the foregoing description, our brake has the qualities,of (first) requiring negligible physical effort by the driver, (second)producing extremely powerful braking action, (third) extremesensitiveness and uniformity in action throughout the entire range ofdegrees of braking action, and (fourth) simple unitary construction andelimination of operating connections between the drivers control deviceand the brake which would require adjustment.

The two first named qualities flow from electrically controlling thebrake and from derivation of power from the motion or momentum of thevehicle to set the brake.

The factors contributing to the third named quality are the characterand construction of the electromagnetic friction device, i. e., themagnet and its armature; the means (in the present; embodiment spring46) for insuring or maintaining a definite or fixed relation between themagnet and its armature at the instant of energization of the magnet soas to provide a substantially invariable air gap (which in the presentinstance is zero at one point at least) and thereby insure an even oruniform flow of magnetic flux at each successive stage of movement ofthe controlling rheostat and avoid sudden or uneven grabbing of thebrake; the construction and arrangement of the parts of theforce-augmenting connection between said friction device and the brakingmeans by which the brake will be set upon a small fraction of onerotation of the wheel and will be instantly and positively restored tobrake released position.

The quality named fourth above resides in the construction andarrangement of the parts in a compact unit which creates or derives itsown brake setting power upon energization of the magnet and requires noconnection to the drivers control device other than a simple electricalconductor.

Extended rigid tests of brakes constructed in accordance with ourinventionover a long period of time and under all conditions, speeds andemergencies of driving have demonstrated for the present invention anease and accuracy of vehicle control and rapidity of deceleration notpossible with any means of braking heretofore known.

This application is a continuation of our prior application Serial No.156,355, filed December 22, 1926.

We claim as our invention:

1. A vehicle brake comprising, in combination, a drum arranged to rotatewith the vehicle wheel to be braked, a pair of brake shoes mountedwithin said drum, cam means located between adjacent end portions ofsaid shoes for expanding them against the inner peripheral surface ofsaid drum, a non-rotatable support closing the open end of said drum, arock shaft journaled in said support and arranged to operate said cammeans, a crank arm on said rock shaft, a peripheral flange carried bysaid drum disposed in a plane substantially perpendicular to the drumaxis, a metallicring mounted opposite said flange, and anelectromagnetic winding in said ring adapted when energized to causefrictional gripping engagement of said ring and said flange, and meansoperatively connecting said ring and the free end of said crank armwhereby oscillation of said ring will expand said shoes.

2. An electric vehicle brake comprising, in combination, a drum arrangedto rotate with the vehicle wheel to be braked, a non-rotatable membercooperating with said drum to provide a closed casing, brake meanswithin said casing, an electromagnet located within said casing andadapted when energized to engage frictionally with a rotating surface onsaid drum, and a force multiplying connection for transmitting movementof said magnet to said brake means, a portion of said connection beinglocated outside of said casing.

3. An electric vehicle brake of the momentum type, compris'hg incombination, a drum rotatable with the wheel to be braked, braking meanswithin said drum, expanding means therefor including a rock shaftextending parallel to the drum axis and disposed near the periphery ofthe drum, an electromagnetically controlled friction device having adriving element rotatable with said drum and an oscillatory drivenelement mounted coaxially of the drum, said elements being adapted forfrictional gripping engagement by a force acting in an axial direction,a crank arm fixed to said rock shaft and extending when inbrake-released position in a direction substantially perpendicular to adiameter through the axes of said drum and rock shaft, and means rigidlyconnecting said driven element to the free end of said crank arm.

4. An electric vehicle brake of the momentum type comprising, incombination, a drum rotatable with the vehicle wheel to be braked, anexpansible braking means within said drum, means carried by said drumand providing an inwardlyfacing friction surface, a substantially rigidmetal ring mounted for oscillatory movement and adapted for frictionalgripping engagement with said surface by a force acting axially of saidring, electromagnetic means for causing such engagement, a rockshaftextending through said ring and spaced from the drum axis, means carried by said rockshaft for expanding said braking means, means operableto apply the actuating force derived through oscillation of said ring ineither direction to said rockshaft including a crank arm fixed: to saidrockshaft, and means normally acting to maintain said ring inbrakereleased position.

5. An electric vehicle brake of the momentum type comprising, incombination, a drum rotatable with the vehicle wheel to be braked, agripping device engageable therewith, a friction device adapted to beoperated by electromagnetic action whereby to derive an actuating forcefrom the motion of said wheel, mechanism for receiving said force andapplying, the same to said gripping device, said mechanismincluding acrank arm mounted for oscillation in a plane perpendicular. to the drumaxis, and means operable upon deenergization of said device afteroscillation of said crank in either direction to apply a force to saidcrank in a direction substantially perpendicular thereto whereby torestore the crank to brake released position.

6. An electric vehicle brake of the momentum type comprising, incombination, a drum mounted on the inner side of the vehicle Wheel to bebraked, and having an external flange portion providing an inwardlyfacing friction surface, a substantially rigid ring mounted oppositesaid surface for oscillation about the drum axis, an electromagneticwinding adapted when energized to cause magnetic attractionof said ringand said flange, a braking means within said drum, expanding meanstherefor spaced a substantial distance from the drum axis, mechanismreceiving the force resulting from the magnetic attraction andfrictional engagement of said ring and flange and operable to apply suchforce with increased mechanical advantage tosaid expanding means, andmeans acting to maintain said ring and said mechanism in brake-releasedposition when said winding is deenergized.

'7. An electric momentum brake for a vehicle wheel supporting an axlecomprising, in combination, a drum rotatable with said wheel, expansi-'ble braking means'within said drum, a friction device having a drivingelement carried by said drum externally thereof and an annular driven[element adapted for frictional gripping engagement with said drivingelement by a force acting along the axis of said drum, a non-rotatablecasing arranged concentrically with said axle and supporting said drivenelement in centered position opposite said driving element and foroscillatory movement, mechanism for applying the rotary power derivedthrough the engagement of said elements and to said braking means, andelectromagnetic means by which the degree of frictional engagementbetween said elements may be variably controlled.

8. An electric momentum brake for a vehicle wheel supporting an axlecomprising, in combination, a drum'carried by said wheel with one endthereof adjacent said wheel, braking means within said drum havingadjacent end portions disposed near the periphery of the drum, a cammember positioned between said end portions and adapted for oscillationabout an axis parallel to said axle whereby to spread said end portions,a crank arm rigid with said cam and extending in a non-radial directionwith respect to said drum when said cam is in brake-released position, apair of annularly arranged friction elements mounted for grippingengagement by the action of a force acting axially of said elements, oneof said elements being carried by said drum so as to rotate therewith,said other element being associated with the free end of said crank armso as to actuate the arm upon oscillation of said driven element ineither direction, and electromagnetic means adapted to be variablyenergized to regulate the degree of frictional pressure between saidelements in setting the brakes.

9. An electric vehicle brake of the momentum type comprising, incombination, a drum which rotates during motion of the vehicle, abraking device engageable therewith, actuating means for said brakingdevice including a crank arm mounted to oscillate in a path notincluding a diameter of said drum, a pair of friction elements adaptedfor gripping engagement by a force acting in a direction axially of saiddrum, one of said elements being operatively associated with the freeend of said crank arm so as to actuate the arm upon oscillation ineither direction, and electromagnetic means by which the degree ofgripping engagement between said elements may be variably controlled.

10. An electric momentum brake for a vehicle wheel supporting an axle, adrum which rotates with said wheel, a braking device adapted formovement into engagement with said drum and having adjacent endportions, means associated with said end portions and operable to applysaid device to said drum, said means including a crank arm normallyextending in a non-radial direction with respect to said drum axiswhenin brake-released position, said arm being mounted to oscillate about afixed axis which is spaced from and extends-parallel to said axle, twoannular friction elements adapted for gripping engagement by the actionof a force acting axially of said drum, one of said elements having afriction surface which rotates with said drum, said other element beingconnected to the free end of said crank arm so as to apply thereto anactuating force derived through the engagement of said elements, andelectromagnetic means by which the degree of gripping engagement betweensaid elements may be variably controlled.

11. An electric momentum brake for a wheel supporting a vehicle axlecomprising, in combination, a drum which rotates about said axle duringmotion of said wheel, segmental brake members arranged around said axlewithin said drum, an expanding device spaced from said axle and adaptedto work against adjacent end portions of said members, an outwardlyprojecting substantially radial flange carried by said drum andproviding an annular friction surface of narrow radial width which facesinwardly relative to said wheel, an annulus of substantially the sameradial width as said surface supported opposite the surface forfrictional engagement therewith, an electromagnetic winding adapted whenenergized to cause attachment of said annulus magnetically to saidsurface, and'force-multiplying mechanism connecting said annulus andsaid expanding means.

12. An electric momentum brake for a ,wheel supporting a vehicle axle,comprising, in combination, a drum rotatable with said wheel andarranged concentrically about said axle, brake means arranged withinsaid drum about said axle and having adjacent separable end portions,means operable to spread said end portions whereby to expand said brakemeans against said drum, a driving element carried by said ,drum andhaving a friction surface of narrow radial width and of substantiallythe same diameter as said drum, an oscillatory driven element having afriction surface of substantially the same diameter and radial width assaid first mentioned surface and adapted for gripping engagementtherewith, electromagnetic means adapted when energized to causegripping engagement of said elements, force-augmenting mechanismconnecting said driven element and said expanding means, and meansoperable to restore said driven element and said mechanism tobrake-released position after deenergization of said electromagneticmeans.

13. An electric momentum brake for a vehicle having, in combination,friction brake members adapted when engaged to check the motion of saidvehicle, and an actuating mechanism comprising a friction element whichnormally rotates when the vehicle is in motion, an oscillatory frictionelement connected to one of said friction members for operating thesame, an electromagnetic winding associated with one of said elementsand adapted when energized to draw the elements into frictional grippingengagement and thereby cause oscillation of said driven element, andyieldable means acting on one of said elements and normally tending tourge said elements resiliently toward each other.

14. An electric momentum brake for a vehicle having, in combination,friction brake members adapted when engaged to check the motion of saidvehicle, a friction element which rotates when said vehicle is inmotion, a driven friction element adapted for engagement with saidrotating element and when so engaged to derive an actuating force fromthe momentum of the vehicle and apply such force to one of said brakemembers, an electrical winding adapted when energized to magnetize saidelements and thereby causethem to be drawn into gripping engagement, andmeans supplemental to said winding acting to urge said elements intoclose proximity to each other and thereby decrease the reluctance of themagnetic circuit through said elements. V

15. An electric momentum brake for a vehicle having, in combination, arevoluble member, a,

braking device adapted for engagement with said member whereby tocontrol the motion of said vehicle, a friction element which normallyrotates simultaneously with said member, a second friction elementadapted for engagement with said first mentioned element and operativelyconnected to said braking device for actuating the same, an electricwinding associated with one of said elements and forming therewith anelectromagnet of which said other element is the armature, and meansnormally operating to maintain intimate mechanical contact between saidelements and thereby provide a substantially closed metallic circuit forthe flow of magnetic flux produced upon the initial energization of saidwinding.

16. An electromagnetic brake for a vehicle wheel having, in combination,a magnetic element rotatable with said wheel and having an annularfriction surface spaced a substantial distance from the wheel axis anddisposed in a. plane substantially perpendicular to said axis, a secondmagnetic element mounted opposite said first mentioned element andhaving a friction surface adapted for coacting engagement with saidother surface, an electromagnetic winding carried by one of .saidelements and adapted when energized to cause magnetic attraction whichproduces a force acting in an axial direction thereby causing grippingengagement of said elements, and means supplemental to said windingacting automatically to urge said elements into intimate mechanicalcontact with each other and thereby decrease the reluctance of themagnetic circuit through said elements.

17. An electric vehicle brake of the momentum type comprising, incombination, a drum which rotates during motion of the vehicle, brakingmeans mounted within the drum and having adjacent end portions locatednear the periphery of the drum, means located near and cooperating withsaid end portions for expanding said braking means, a magnetic elementmounted to rotate with said drum and having an annular friction surfacedisposed externally of the drum, a driven magnetic element mounted foroscillatory movement and adapted for frictional engagement with saidannular surface, electromagnetic means adapted when energized tomagnetize said elements and thereby cause gripping engagement thereof,means operative to transmit force from said driven element to saidexpanding means, and means acting to restore said oscillatory frictionelement to brake released position.

18. An electric vehicle brake of the momentum type comprising, incombination, a drum ar-' ranged to bemounted on the inner side of thevehicle wheel to'be braked with one end thereof closely adjacent to saidwheel, braking means mounted within the drum and having adjacent endportions located near the periphery of the drum, means located near andcooperating with said end portions for expanding said braking means, anelement mounted to rotate with said drum and having an annular frictionsurface, a driven element mounted for oscillatory movement and adaptedfor frictional gripping engagement with said annular surface,electromagnetic means adapted when energized to produce a force actingin an axial direction thereby causing such engagement, and meansoperative to transmit force from said driven element to said expandingmeans with increased mechanical advantage.

19. An electric vehicle brake of the momentum type comprising, incombination, a drum arranged to be mounted on the inner side of thevehicle wheel to be braked with one end thereof closely adjacent to saidwheel, braking means mounted within the drum and having adjacent endportions located near the periphery of the drum, means located near andcoperating with said end portions for expanding said braking means, anelement mounted to rotate with said drum and having an annular frictionsurface disposed externally of the drum, a driven element mounted foroscillatory movement and adapted for frictional gripping engagement withsaid annular surface, electromagnetic means adapted when energized tocause such engagement, and means operative to transmit force from saiddriven element to said expanding means.

20. An electric vehicle brake of the momentum type comprising, incombination, a drum which rotates during the motion of the vehicle,friction brake means mounted within said drum and having adjacent endportions, a non-rotatable support, a member mounted on said support tooscillate on an axis which extends parallel to and is spaced from thedrum axis, said member having means operable upon oscillation of themember to spread said end portions and thereby expand said brake meansinto engagement with said drum, two friction elements having opposedsurfaces disposed externally of the axis of said member and adapted tobe frictionally gripped together, one of said elements being carried bysaid drum, the other element being adapted for oscillation about thedrum axis and operatively connected to said member for actuating thesame, electromagnetic means adapted when energized to cause frictionalengagement of said elements, control means by which the flow of currentin said electromagnetic means may be varied in successive increments toregulate the degree of gripping force between said elements, and meansfor restoring the said last mentioned element and said expanding meansto brake-released position when the flow of current in saidelectromagnetic means is interrupted.

21. An electric vehicle brake of the momentum type comprising, incombination, a rotatable drum, expansible brake means within said drum,expanding means therefor, actuating mechanism for said expanding meansincluding two friction elements arranged for gripping engagement oneadapted to rotate simultaneously with said drum, the other beingoperatively connected to said expanding means for actuating the same, anelectromagnetic winding adapted when energized to cause grippingengagement between said elements, spring means normally acting tocontract said brake means within said drum, and supplemental springmeans acting on said mechanism for restoring the mechanism tobrakereleased position upon the de-energization of said winding.

22. An electric vehicle brake of the momentum type comprising,in'combination, a drum which rotates during motion of the vehicle wheelto be braked, expansible brake means within said drum, spring meansacting to contract said brake means, two magnetic elements adapted to bedrawn into frictional gripping engagement upon the energization of anelectromagnetic winding carried by one of said elements, a second springmeans tending to resiliently urge said elements into close proximity toeach other, one of said elements being arranged to rotate simultaneouslywith said drum, said other element being mounted for oscillation Whenmagnetically attracted to said rotating element, means connected to saidoscillatory element and adapted to apply the force derived through themedium of said elements to said brake means with increased leverage soas to expand the same, and supplemental spring means operable tomaintain said oscillatory element and said force augumenting means inbrake-released position when said winding is deenergized.

23. An electric vehicle brake of the momentum type comprising, incombination, a brake drum which rotates with the vehicle wheel to bebraked, friction braking means movable into gripping engagement withsaid drum, means operable upon a small fraction of one revolution of thevehicle wheel in either direction for moving said braking means intobraking engagement with said drum, the last mentioned means including anelectromagnetically operated friction device deriving an actuating forcefrom the motion of the vehicle and arrangedto transmit saidforce to saidbrakeapplying means, the coacting magnetic elements of said device beingunrestrained from movement toward each other, and means acting toprevent rotation of the driven element of said device by reason of itsfrictional engagement with the driving element except when the saiddevice is magnetized.

24. An electric vehicle brake of the momentum type comprising, incombination, a member which rotates during motion of the vehicle, arelatively non-rotatable device arranged for braking engagement withsaid member, an annular element composed of magnetic material andnormally rotating simultaneously with said member, a second annularelement mounted for oscillatory movement and arranged for frictionalgripping engagement with said first mentioned element by a force actingin an axial direction, a winding comprising a coiled electricalconductor extending continuously in a series of turns to form an annulusand disposed in a single annular recess in one of said elements so thatwhen energized said winding will constitute the inner and outer portionsof that element as magnetic poles of opposite polarity, control means bywhich the flow of current in said winding may be varied in successiveincrements to regulate the degree of attractive force between saidelements, means connecting said second element and said brake device andadapted to apply the force derived through the frictional engagement ofsaid elements to said device with increased leverage, and means forrestoring said last mentioned element and said connecting means tobrake-released position when the flow of current in said winding isinterrupted.

25. An electric vehicle brake of the momentum type comprising, incombination, a drum mounted on the vehicle wheel to be braked, frictionmeans within said drum, expanding means therefor, a member cooperatingwith said drum to provide a closed casing, mechanism including a pair ofelectromagnetically operable -friction elements adapted to derive anactuating force from the motion of said drum for application to saidexpanding means, an insulated electrical conductor having anon-rotatable mounting on said member and having a connection withinsaid casing to the magetizing winding for said elements which allows foroscillation of the elements.

26. An electric vehicle brake of the momentum type comprising, incombination, a drum carried by the vehicle wheel to be braked; brakingmeans adapted for engagement therewith; a driving friction elementcarried by said drum; a driven element adapted for frictional grippingengagement with said driving element; mechanism operable to transmit theangular motion of said driven element'to said braking means; anonrotatable member closing the open end of said drum and supportingsaid braking means, said driven element and said mechanism; anelectromagnetic winding carried by one of said elements and adapted whenenergized to cause frictional engagement of said elements; and meansproviding an energizing circuit for said winding including a contactterminal non-rotatably mounted on said member and having an electricalconnection with said winding which allows for movement of said windingin the operation of said elements.

27. A momentum brake for a vehicle wheel supporting an axle comprising,in combination, a drum mounted on said wheel, braking -means adapted formovement into engagement with said drum, a driving friction elementcarried by said drum externally thereof and providing an inwardly facingsurface of relatively narrow radial width and of a diametercorresponding approximately to that of said drum, a substantially rigidmetallic ring constituting a driven element and having a surfacecorresponding in radial width to and adapted for engagement with saidfirst mentioned surface, a relatively stationary support having bearingsurfaces disposed a substantial distance from said axle for supportingsaid ring concentric with said drum for oscillatory movement whenengaged by said driving element, means by which the degree of frictionalpressure between said elements may be varied, and mechanism actuated byoscillation of said ring to apply said braking means to said drum.

28. An electromagnetic momentum brake for a vehicle wheel which supportsan axle having a pivoted yoke-type steering knuckle with a wheel spindlethereon, said brake being composed of a single individual unitcomprising, in combination, a drum fixed to and rotatable with saidWheel; braking means arranged to frictionally engage said drum; anelectromagnetically controlled friction device arranged to derive powerfrom the motion of said wheel; a force-augmenting connection betweensaid device and said braking means; said braking means, frictiondevice,and connection being correlated in a compact unit in an annularspace outside of a central space defined by the dimensions of saidsteering knuckle; and an electrical conductor leading from a source ofpower on the vehicle and connected to said friction device forenergizing the latter to create a force solely within said brake "unititself for operating said braking means.

29. An electric momentum brake for a vehicle wheel mounted on ayoke-type steering knuckle which is pivoted to swing on an upright axisadjacent the plane of said wheel, said brake comprising, in combination,a drum carried by said wheel on the inner side thereof; braking meansarranged for engagement with saiddrum; a friction device operable toderive an actuating force from the motion of said wheel including adriving element rotatable with said drum and a 'driven elementengageable frictionally with the III) ing knuckle when the latter ispositioned in conventional relation to the plane of said wheel.

30. In an electric friction brake for a vehicle, the combination offriction braking members and mechanism adapted to derive a force fromthe momentum of the vehicle for actuating said braking means comprisinga magnetic element .mounted on the vehicle to rotate during motion ofthe latter and having an annular friction face disposed substantiallyvertically, a second magnetic element mounted for angular movement aboutan axis of said rotatable element and having a frictional faceengageable with said rotatable face, one of said elements being mountedfor floating movement along said axis to permit of yielding engagementbetween the elements and thereby compensate for the inherent lateralwobbling of the rotatable element, an electromagnetic winding on one ofsaid elements adapted when energized to produce a force of magneticattraction between the elements whereby said rotatable element willexert a frictional force on said second element tending to move thelatter away from normal brake-released position, means operable totransmit the actuating force thus derived to said braking means, and aspring acting constantly in a direction generally longitudinally of saidrotational'axis to urge said floating element toward the other elementand thereby maintain intimate contact between said faces while saidwinding is deenergized.

31. An electric friction brake having, in combination, a magneticelement having an annular friction surface which rotates during motionof the part whose motion is to be controlled, a second magnetic elementhaving a friction surface adapted for gripping engagement with saidfirst mentioned surface, one of said elements having concentric polesfacing the other element, a winding mounted between said poles andadapted whenenergized to create a magnetic flux in the magnetic circuitthrough said poles and the opposing element thereby causing grippingengagement of said friction surfaces, and means acting constantly whilesaid winding is denergized to maintain the reluctance of said magneticcircuit substantially uniform thereby preventing variation of thereluctance by the inherent lateral wobbling of the rotatable element.

32. In an electric friction brake for a vehicle, a pair'of rings ofmagnetic material having opposed annular faces, one of said rings beingrotatable during motion of the vehicle, a winding carried by one of saidrings and adapted when energized to create a magnetic flux which threadsthe ferro-magnetic circuit through the faces of said rings therebycausing frictional gripping engagement the magnitude of which determinesthe degree of braking action, control means governing the closure of anenergizing circuit through said winding, and means supplemental to saidwinding acting automatically to insure the existence of mechanicalcontact between the engaging portions of said faces coincident with theapplication of current to said winding by said control means whereby theoperation of the brake in response to said control means is unaffectedby the lateral wobbling of said rotatable ring.

33. In an electric friction brake, the combination of cooperatingbraking members and mecha- V .nism adapted to derive a force from themomentum of the part to be braked for actuating one of said memberscomprising a rotatable magnetic element having an annular friction face,a second magnetic element mounted for some degree of angular movementand having a frictional face engageable with the face of said rotatableelement, one of said elements being mounted for floating movement tocompensate for the lateral wobbling of the rotatable element, anelectromagnetic winding on one of said elements adapted when energizedto produce a force of magnetic attraction between the elements wherebysaid rotatable element will exert a frictional force on the secondelement tending to move the latter angularly away from normalbrake-released position, means operable to transmit the angular movementof the second element to one of said braking members, means constantlyacting to urge said floating element toward the other element andthereby yieldably maintain continuous contact between said faces whilesaid electromagnet is deenergized, and spring means overcoming thetendency of said second element to move away from brake-releasedposition as an incident to said continuous contact.

34. In an electrically controlled momentum actuator for a frictionbrake, the combination of two annular magnetic elementshaving frictionfaces arranged for axial gripping engagement, one of said elements beingmounted to rotate during motion of the part to be braked, the otherbeing mounted for limited angular movement but normally held underspring effect against such movement and thereby maintained in a normalbrakereleased position, a magnetic winding carried by one of saidelements and adapted when energized to produce magnetic attraction ofthe elements whereby said second element overcomes said spring effectand moves through a limited angular distance to actuate the brake, andmeans for maintaining a substantially uniform reluctance of the magneticcircuit through said elements comprising spring means normally actingwhen said winding is deenergized to urge the elements together andmaintain light mechanical contact between their friction faces which isinsufficient to overcome said spring effect tending to hold said secondelement in brake-released position.

35. An electromagnetic friction device having, in combination, twomagnetic elements mounted for relative rotation, means for magnetizingsaid elements to cause attraction toward each other, and means actingautomatically to urge said elements into close proximity and therebydecrease the reluctance of the magnetic circuit through said elements. y

36. An electromagnetic friction device having, in combination, a mainfriction device comprising coacting friction members, and an actuatingmechanism therefor comprising a rotary friction element, a coactingfriction element connected to said friction members to cause engagementof the latter, and an electromagnetic winding associated with one ofsaid elements and adapted when energized to draw the elements intofrictional gripping engagement and thereby cause rotation of saidelements in unison, and yielding means acting on one of said elementsand normally tending to urge said elements toward each other.

3'7. An electromagnetic friction device having, in'combination, a rotarymagnetic element having an annular friction surface, a second magneticelement mounted opposite said first mentioned element and having afriction surface adapted for coacting engagement with said othersurface, an electromagnetic winding carried by one of said elements andadapted when energized to cause magnetic attraction which produces forceacting in an axial direction thereby causing gripping engagement of saidelements, and means supplemental to said winding acting automatically tourge said elements into intimate mechanical contact with each other andthereby decrease the reluctance of the magnetic circuit through saidelements.

38. An electromagnetic friction device having, in combination, a.plurality of friction elements engageable together to frictionallyresist relative 10 rotation, two magnetic elements mounted for relativerotation, means for magnetizing said elements to cause attraction towardeach other, means acting automatically to urge said elements into closeproximity and thereby decrease reluctance of the magnetic circuitthrough said elements, and means operable upon magnetization of saidmagnetic elements to move said friction elements into engagement.

ARTHUR P. WARNER.

ADDI BENJAMIN CADMAN.

